This invention relates to a new method of power opening a top hinged gravity closing and floating opening gate on a dump body mounted on a truck, semi-trailer or full-trailer chassis.
Dump bodies mounted on truck or trailer chassis are used to carry bulk flowable granular or chunk material such as dirt, crushed rock, hot asphalt paving, wet concrete, building or highway demolition debris, etc. from one location to another. The material is normally loaded into the dump body by self-powered machines such as tracked excavators, wheel loaders, backhoes, or from an overhead loading device such as a conveyor, chute or bottom discharge storage bin. The material is constrained within the body by the body floor and sides, a front bulkhead and a rear top hinged gate. The top of the body is open during loading and sometimes during unloading, but it is closed during transportation to the dump site. Normally the end dump body discharges its load into a pile or onto a conveyor mechanism which then moves the material way from the dump body. The method used to discharge the material from the dump body is to position the rear of the body containing the gate at the location of desired discharge, unlock the bottom latch of the top hinged gate so it is free to open from either the contents pressing against it or by gravity as the rear hinged body is rotated. The front of the body is raised until the floor of the body is tilted steeply enough that the contents of the body slide rearward and downward against the unlatched hinged gate which then opens as required from the pressure of the sliding contents and allows the contents to slide out of the body onto the ground or conveyor stem.
When the discharge is complete, the end dump body is pulled clear of the discharged contents pile during which the gate is free to ride over or float over the pile until it clears the pile. About the same time as the body is pulled clear of the pile, the dump body is lowered to its horizontal position, the gate closes by gravity because the hinge is located forward of the gate, the latch is locked and the truck is driven to the next loading site to start the cycle over.
Under certain circumstances it is desirable to have a powered mechanism open the gate to approximately parallel to the body floor before the body is rotated into its steep dump angle. This occurs for example when the rear of the body gets so close to the discharge surface before the contents start to slide out that the hinged gate will not clear or is driven into the discharge surface. In this case, the load discharge will be impeded by the gate which can result in damage to the gate. Another scenario occurs when the contents are large and heavy, such as large boulders, that when they start sliding or tumbling rearward and downward against the gate, the gate may be damaged or destroyed by impact before it can be forced open. At the present time, this need to open the gate to approximately its maximum discharge opening which occurs at the point where the gate face aligns with the body floor, is accomplished by a body mounted air, hydraulic or electric powered actuator lift mechanism which lifts the gate hinge arms until the gate face is parallel to the body floor. This power hinge lift mechanism is activated manually after the gate latch is unlocked or automatically by a delayed action valve that first unlocks the latch then powers the gate open and the reverse when the gate is lowered and then latched. Since the gate must be free to open further than the power actuator lifts it as it rides over the discharge pile, the gate powered lift mechanism is not connected directly to the hinge arms, but merely lifts the hinge arm via a protrusion on the hinge arm. The lift arm hinges about the same hinge center as the gate hinge so that it follows the gate as it hinges under power. These gate lift arm power actuators are located forward of the gate along the sides of the dump body in either a horizontal or vertical position. Since the dump bodies are primarily loaded from the side by large machines, the side mounted cylinders are very vulnerable to damage from both the loading vehicle and from the loaded material which frequently tumbles onto the top of the body side during loading and dumping. The typical solution for this vulnerability is to fasten heavy guards around the actuators or to locate the actuators within the body rear structural frame. Both of these guarded locations work satisfactorily, but because maximizing the cubic volume of the body is always an important objective with dump bodies, and since the overall width of a truck or trailer body is restricted by state and federal regulations, the power actuators are restricted to small cross section which limits the force they can exert and since the work they can do is defined by force times distance, they require a long stroke to have enough power to lift the weight of the gate. This long stroke require a long heavy guard to protect each actuator. If the gate is very large and heavy, it is not possible to fit a large enough actuator to lift the gate. Another problem that occurs is that the actuator and its guard and the lift mechanism usually extends the full legal width of the trailer in order to maximize the dump body width but most states have enacted load covering regulations to prevent the air from aspirating solid particles out to the body during highway transport which results in damage to other vehicles close to the end dump body. These load covering devices also require a mechanism that is outside of the body overall width to function properly. This means that they have to be wider than the guards over the gate hinge power actuators and the lift mechanism or must stop covering the load at some distance from the gate and a secondary covering device installed inside the body to cover this gap. This increases complexity, cost and time to manipulate during each load transport cycle.
Another problem is that at the rear of the dump body, a strong frame is required to prevent the body from spreading from the outward pressure of the load piled against the side of the discharge opening. This frame is usually the widest part of the body structure and accordingly there is no room for a powered lift mechanism outside of this frame and so the lift mechanism must be forward of this frame and thus so must the gate hinge. The more forward the gate hinge, the more power it takes to open and the greater the force exerted on the gate and hinge by the sculpting of the pile as the gate is dragged across it. Since the required lift forces get very large as the gate hinge moves forward, the gate and hinge must be built very robust and thus becomes heavy which exacerbates the limited power available from the size restricted body mounted actuators and lift mechanism.
An object of this invention is to provide a top hinged gravity, floating and power self-opening gate for a dump body which fulfils the above needs.
A further object of this invention is to provide a gate which can easily be operated and is effective in its operation.
In accordance with this invention the top-hinged gravity and floating opening gate assembly includes a gate for selectively opening and closing the discharge opening of a dump body. At least one hinge arm is mounted to the gate. The hinge arm is pivotally mounted to a first pivot structure located above and forward of the gate. A gravity release lever is pivotally mounted to the first pivot structure. A variable length power actuator such as a piston/cylinder assembly is mounted to the gate. A second pivot structure displaced from the first pivot structure is secured to the gravity release lever. A linkage assembly may be connected to the variable length power actuator and be pivotally mounted to the second pivot structure. When the actuator is increased in its length the gate rotates from its closed position to an open position which would be generally perpendicular to the closed position and parallel to the floor of the dump body. The gravity release lever permits the gate to rotate beyond that open position in response to an object contacting the gate.
In a preferred practice of this invention each side of the gate is provided with a hinge arm and with a gravity release lever with the associated pivot structures. Each side may be provided with its own variable length power actuator or a single variable length power actuator may be used for powering both sides.
The variable length power actuator may be connected to the second pivot structure by a linkage assembly which may include a crank arm pivotally connected to the actuator with the crank arm being rigidly secured to a connector arm which in turn is pivotally connected to a connector link pivotally mounted to the second pivot structure.